Windows: download busybox-win32 during make win-extras

copy it to echo.exe and printf.exe during make dist
This allows test/spawn.jl to succeed on Windows, since echo and printf
are only included as shell scripts in msysgit (and an echo.bat in
contrib/windows), but libuv cannot spawn shell or bat scripts.
In-place filt!, allow passing initial filter state

This redefines `filt` as `filt!` with a few modifications to perform its
filtering in-place. `filt` is defined as a simple wrapper, copying the vectors
that `filt!` modifies.

Further, both methods now allow an optional argument for the initial filter
state vector. This vector is modified in-place in `filt!`.
Be smarter about the initial filter state

Compute an initial state for filt such that its response to a step function is
steady state.
Revert "Be smarter about the initial filter state"

This reverts commit 19ba34c001152977d4fc011c75e1e08bb260aacf.
Fix copy! for ranges
NEWS and doc for filt state and filt!
Add Apache License as an option for Pkg.generate
Update generate.jl
print invalid-identifier symbols as symbol("..."); fixes #7188
added test case for #7188
isidentifier paranoia: don't assume id_char ⊆ id_start_char
don't quote operators, and do quote end keyword, in symbol display as suggested by #7531
linrange: wrap definition for readibility (cosmetic).
Add a 3-argument method for scale! for scalars

Just like as scale! allows a pre-allocated argument for scaling a matrix by a
vector, this allows specifying a third array as the output for scaling by
scalars.
Refactor filt! to use an output argument

- No longer modifies the filter state in place, instead uses a copy
REPL: allow modes to be made sticky.

For example, to make shell mode sticky, which was my motivation, do

	try
	    Base.active_repl.interface.modes[2].sticky = true
	end

in your ~/.juliarc.jl file.
Bump openblas to 0.2.10.rc2
Merge pull request #7540 from stevengj/printsymbol

print invalid-identifier symbols as symbol("..."); fixes #7188
checksums for openblas-v0.2.10.rc2
Use strip instead of chop in openblas_get_config()

As of https://github.com/xianyi/OpenBLAS/commit/552119c48429c76a701600d05d3a1f472a41c65c, OpenBLAS now returns the processor family at the end of the config string (yay!), without a trailing whitespace. Using strip makes this compatible with both new and old versions of OpenBLAS.